Experimental and Theoretical Studies on Acid Corrosion Inhibition of API 5L X70 Steel with Novel 1-N-α-d-Glucopyranosyl-1H-1,2,3-Triazole Xanthines.

A series of novel 1-N-α-d-glucopyranosyl-1H-1,2,3-triazole xanthines was synthesized from azido sugars (glucose, galactose, and lactose) and propargyl xanthines (theophylline and theobromine) using a typical copper (I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition. The corrosion inhibition activities of these new carbohydrate-xanthine compounds were evaluated by studying the corrosion of API 5 L X70 steel in a 1 M HCl medium. The results showed that, at 10 ppm, a 90% inhibition efficiency was reached by electrochemical impedance spectroscopy. The inhibitory efficiency of these molecules is explained by means of quantum chemical calculations of the protonated species with the solvent effect, which seems to better represent the actual situation of the experimental conditions. Some quantum chemical parameters were analyzed to characterize the inhibition performance of the tested molecules.

A General Use QSAR-ARX Model to Predict the Corrosion Inhibition Efficiency of Drugs in Terms of Quantum Mechanical Descriptors and Experimental Comparison for Lidocaine.

A study of 250 commercial drugs to act as corrosion inhibitors on steel has been developed by applying the quantitative structure-activity relationship (QSAR) paradigm. Hard-soft acid-base (HSAB) descriptors were used to establish a mathematical model to predict the corrosion inhibition efficiency (IE%) of several commercial drugs on steel surfaces. These descriptors were calculated through third-order density-functional tight binding (DFTB) methods. The mathematical modeling was carried out through autoregressive with exogenous inputs (ARX) framework and tested by fivefold cross-validation. Another set of drugs was used as an external validation, obtaining SD, RMSE, and MSE, obtaining 6.76%, 3.89%, 7.03%, and 49.47%, respectively. With a predicted value of IE% = 87.51%, lidocaine was selected to perform a final comparison with experimental results. By the first time, this drug obtained a maximum IE%, determined experimentally by electrochemical impedance spectroscopy measurements at 100 ppm concentration, of about 92.5%, which stands within limits of 1 SD from the predicted ARX model value. From the qualitative perspective, several potential trends have emerged from the estimated values. Among them, macrolides, alkaloids from Rauwolfia species, cephalosporin, and rifamycin antibiotics are expected to exhibit high IE% on steel surfaces. Additionally, IE% increases as the energy of HOMO decreases. The highest efficiency is obtained in case of the molecules with the highest ω and ΔN values. The most efficient drugs are found with pKa ranging from 1.70 to 9.46. The drugs recurrently exhibit aromatic rings, carbonyl, and hydroxyl groups with the highest IE% values.

4-Phenylcoumarin (4-PC) Glucoside from Exostema caribaeum as Corrosion Inhibitor in 3% NaCl Saturated with CO2 in AISI 1018 Steel: Experimental and Theoretical Study.

The corrosion inhibition of 5-O-ß-D-glucopyranosyl-7-methoxy-3',4'-dihydroxy-4-phenylcoumarin (4-PC) in AISI 1018 steel immersed in 3% NaCl + CO2 was studied by electrochemical impedance spectroscopy (EIS). The results showed that, at just 10 ppm, 4-PC exerted protection against corrosion with Õ² = 90% and 97% at 100 rpm. At static conditions, the polarization curves indicated that, at 5 ppm, the inhibitor presented anodic behavior, while at 10 and 50 ppm, there was a cathodic-type inhibitor. The inhibitor adsorption was demonstrated to be chemisorption, according to the Langmuir isotherm for 100 and 500 rpm. By means of SEM-EDS, the corrosion inhibition was demonstrated, as well as the fact that the organic compound was effective for up to 72 h of immersion. At static conditions, dispersion-corrected density functional theory results reveal that the chemical bonds established by the phenyl group of 4-PC are responsible of the chemisorption on the steel surface. According with Fukui reactivity indices, the molecules adsorbed on the metal surface provide a protective cover against nucleophilic and electrophilic attacks, pointing to the corrosion inhibition properties of 4-PC.

Multicomponent Synthesis and Evaluation of New 1,2,3-Triazole Derivatives of Dihydropyrimidinones as Acidic Corrosion Inhibitors for Steel.

An efficient one-pot synthesis of 1,2,3-triazole derivatives of dihydropyrimidinones has been developed using two multicomponent reactions. The aldehyde-1,2,3-triazoles were obtained in good yields from in situ-generated organic azides and O-propargylbenzaldehyde. The target heterocycles were synthesized through the Biginelli reaction in which the aldehyde-1,2,3-triazoles reacted with ethyl acetoacetate and urea in the presence of Ce(OTf)3 as the catalyst. The corrosion inhibition of steel grade API 5 L X52 in 1 M HCl by the synthesized compounds was investigated using the electrochemical impedance spectroscopy technique. The measurements revealed that these heterocycles are promising candidates to inhibit acidic corrosion of steel.

Multicomponent click synthesis of new 1,2,3-triazole derivatives of pyrimidine nucleobases: promising acidic corrosion inhibitors for steel.

A series of new mono-1,2,3-triazole derivatives of pyrimidine nucleobases were synthesized by one-pot copper(I)-catalyzed 1,3-dipolar cycloaddition reactions between N-1-propargyluracil and thymine, sodium azide and several benzyl halides. The desired heterocyclic compounds were obtained in good yields and characterized by NMR, IR, and high resolution mass spectrometry. These compounds were investigated as corrosion inhibitors for steel in 1 M HCl solution, using electrochemical impedance spectroscopy (EIS) technique. The results indicate that these heterocyclic compounds are promising acidic corrosion inhibitors for steel.

Synthesis of new 1,2,3-triazole derivatives of uracil and thymine with potential inhibitory activity against acidic corrosion of steels.

Ten 1,4-disubstituted 1,2,3-triazoles were synthesized from one of 1-(azido-methyl)benzene, 1-(azidomethyl)-4-fluorobenzene, 1-(azidomethyl)-4-chlorobenzene, 1-(azidomethyl)-4-bromobenzene or 1-(azidomethyl)-4-iodobenzene, generated in situ from sodium azide and the corresponding benzyl halide, and dipropargyl uracil or dipropargyl thymine. Optimal experimental conditions were established for the conventional click chemistry. The corrosion inhibiting properties of some of these compounds, which were determined by means of an electrochemical technique, are also presented.

Study of SCC of X70 Steel Immersed in Simulated Soil Solution at Different pH by EIS.

An electrochemical study of stress corrosion cracking (SCC) of API X70 steel in a simulated soil solution at different pH values (3, 8 and 10) was carried out. The stress conditions were implemented by slow strain rate stress test (SSRT) and the SCC process was simultaneously monitored by electrochemical impedance spectroscopy (EIS). Fracture surface analysis and corrosion product analysis were performed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that the susceptibility to SCC was higher as the pH decreases. In the acid solution, hydrogen evolution can occur by H+ and H2CO3 reduction, and more atomic hydrogen can diffuse into the steel, producing embrittlement. EIS results indicated that the anodic dissolution contributed to SCC process by reducing the charge transfer resistances during the SSRT test. While SEM micrographs shown a general corrosion morphology on the longitudinal surface of samples. At higher pH (pH 8 and pH 10), the SCC susceptibility was lower, which it is attributed to the presence of corrosion products film, which could have limited the process. Using the angle phase (φ) value it was determined that the cracking process started at a point close to the yield strength (YS).

Adsorption and corrosion inhibition behaviour of new theophylline-triazole-based derivatives for steel in acidic medium.

The design and synthesis of a series of theophylline derivatives containing 1,2,3-triazole moieties are presented. The corrosion inhibition activities of these new triazole-theophylline compounds were evaluated by studying the corrosion of API 5 L X52 steel in 1 M HCl medium. The results showed that an increase in the concentration of the theophylline-triazole derivatives also increases the charge transference resistance (R ct) value, enhancing inhibition efficiency and decreasing the corrosion process. The electrochemical impedance spectroscopy under static conditions studies revealed that the best inhibition efficiencies (approx. 90%) at 50 ppm are presented by the all-substituted compounds. According to the Langmuir isotherm, the compounds 4 and 5 analysed exhibit physisorption-chemisorption process, with exception of the hydrogen 3, bromo 6 and iodo 7 substituted compounds, which exhibit chemisorption process. The corrosion when submerging a steel bar in 1 M HCl was studied using SEM-EDS. This experiment showed that the corrosion process decreases considerably in the presence of 50 ppm of the organic inhibitors. Finally, the theoretical study showed a correlation between EHOMO, hardness (η), electrophilicity (W), atomic charge and the inhibition efficiency in which the iodo 7 substituted compound presents the best inhibitor behaviour.